Heat curable polyglycidyl aromatic amine encapsulants

Abstract

A highly fluid, solventless heat curable resin is formulated from an admixture comprising a polyglycidyl aromatic amine, a polycarboxylic acid anhydride curing agent, and a curing accelerator. The heat curable formulation exhibits low viscosity and is useful as an encapsulant and insulation for electrical members exposed to high electrical stress. Magnetic coils encapsulated with the cured formulation resist corona discharge at electrical stresses in excess of 2100 volts per mil.

What is claimed is: 
     
       1. A method for encapsulating an electrical component to provide resistance to corona discharge at electrical stresses of about 2100 volts per mil or more in said component comprising: (a) impregnating said component with a low viscosity, heat curable composition comprising an uncured polyglycidyl aromatic amine, a polycarboxylic acid anhydride curing agent, and a chosen curing accelerator; and   (b) curing said composition to form an encapsulating layer on said component, said layer being capable of withstanding electric stress of at least 2100 volts per mil.   
     
     
       2. The method of claim 1 wherein said polyglycidyl aromatic amine is selected from the group consisting of diglycidylaniline, diglycidyl orthotoluidine, tetraglycidyl metaxylylene diamine, and mixtures thereof. 
     
     
       3. The method of claim 1 wherein said curing agent is selected from the group consisting of nadic methyl anhydride, methyl tetrahydrophthalic anhydride, and methyl hexahydrophthalic anhydride. 
     
     
       4. The method of claim 1 wherein said curing accelerator is selected from the group consisting of stannous octoate and 2-ethyl-4-methyl imidazole. 
     
     
       5. An encapsulated electrical component capable of withstanding electric stress of at least 2100 volts per mil comprising the electrical component having adhered thereon an encapsulating layer formed by the method of claim 1. 
     
     
       6. The method of claim 1 wherein the polycarboxylic acid anhydride is present in sufficient quantity to react with from about 60 to about 90 percent of the epoxide groups in said polyglycidyl aromatic amine. 
     
     
       7. The method of claim 1 wherein said curing accelerator is present in the amount of about 0 to about 3 percent, by weight. 
     
     
       8. The method of claim 1 wherein: (a) said uncured polyglycidyl aromatic amine is diglycidyl aniline and is present in the amount of about 100 parts per hundred resin by weight;   (b) said curing agent is methyl tetrahydrophthalic anhydride and is present in the amount of about 114 parts per hundred resin by weight; and   (c) said curing accelerator is stannous octoate and is present in the amount of about 3 parts per hundred resin by weight.   
     
     
       9. The method of claim 1 wherein: (a) said uncured polyglycidyl aromatic amine is diglycidyl orthotoluidine and is present in the amount of about 100 parts per hundred resin by weight;   (b) said curing agent is nadic methyl anhydride and is present in the amount of about 100 parts per hundred resin by weight; and   (c) said curing accelerator is 2-ethyl-4-methyl imidazole and is present in the amount of about 2 parts per hundred resin by weight.